1. Field of the Invention
The field relates to a driving device (actuator) for driving a displacement object, or driven member, by use of a surface-deforming element such as an electromechanical transducer element.
2. Description of the Related Art
Conventionally, proposals have been made in JP-A-4-69070 and JP-A-7-298654 on the arts for driving a lens or the like used for various optical apparatuses, precision instruments, and video apparatuses, etc., such as cameras, overhead projectors, binocular glasses, copiers, plotters and X-Y drive tables. Those have already been realized in practical application. FIGS. 16A-16C illustrate the disclosure in JP-A-4-69070 wherein FIG. 16A is a schematic view of a driving device while FIGS. 16B and 16C show a relationship between a voltage and a time. The lens driver shown in FIG. 16A has a lens barrel 101 supporting a lens and a guide bar 103 supporting the lens barrel 101 and guiding it in an optical-axis direction. The guide bar 103 is passed through a fork 101f formed in a support 101e extending from the lens barrel 101, to support and guide the lens barrel 101.
Meanwhile, a driving rod 117 is provided serving also as a lens-barrel support member for driving the lens barrel 101 axially, to support the lens barrel 101 together with the support 101e. The driving rod 117 is inserted in holes 13b and 13d formed respectively in rises 113a and 113c of a driving-rod support member 113, thus being able to move axially. Meanwhile, the driving rod 117 extends through the holes 101b and 101d formed at both ends 101a and 101c of a squared-U portion 101k extending from the lens barrel 101 opposite to the support 101e. Furthermore, the driving rod 117 has a rear end fixed to a front end of a piezoelectric element 112. The piezoelectric element 112 has a rear end fixed to another rise 113e of the driving-rod support member 113.
Furthermore, a leaf spring 114 is attached to both ends 101a and 101c of the lens barrel 101 from below by screws 115 and 116. The leaf spring 114 is parallel with the driving rod 117 and contains a friction portion 114c in the middle projecting upward. By a contact of the friction portion 114c with the driving rod 117, friction occurs between the lens barrel 101 and the driving rod 117, making it possible to drive the lens barrel 101. Friction is caused by a spring pressure of the leaf spring 114.
FIGS. 16B and 16C illustrate voltage waveforms to be applied to the piezoelectric element 112, wherein FIG. 16B shows a voltage waveform to be applied upon moving the lens barrel 101 rightward in FIG. 16A while FIG. 16C shows a voltage waveform to be applied upon moving it leftward. When a voltage waveform shown in FIG. 16B is applied to the piezoelectric element 112, the piezoelectric element 112 abruptly expands in a sharp rise from voltage A to voltage B. At the same time, the driving rod 117 also moves leftward in FIG. 16A by an amount equal to the elongation of the piezoelectric element 112. However, the lens barrel 101 moves less than the driving rod 117 because of its inertia. Conversely, during a slow change from voltage C to voltage A, the piezoelectric element 112 contracts (returns) slowly. By a frictional force between the lens barrel 101 and driving rod 117 and a frictional force between the leaf spring 114 and driving rod 117, the lens barrel 101 is moved rightward in FIG. 16A. When the lens barrel 101 needs to be moved leftward in FIG. 16A, a voltage with a waveform as shown in FIG. 16C is applied to the piezoelectric element 112, thereby causing it to move in opposite direction. Additionally, the driving device disclosed in JP-A-7-298654 is structured, in JP-A-4-69070, to readily exchange parts and make a repair upon a failure or so on the driving side, whose basic driving mechanism is similar to that of JP-A-4-69070.
Furthermore, JP-A-8-207755 discloses an in-bore moving device (actuator) having a surface-deforming element 200 such as a piezoelectric bimorph having a radius of curvature changing with an applied voltage, a weight 202 fixed in the center of the surface-deforming element 200, clamp legs 204 fixedly held by an outer periphery of the surface-deforming element 200 and abutting against an inner wall W forming a surrounding hole, and control means for supplying an applied voltage having a regulated waveform to the surface-deforming element 200. In this actuator, a driving element and a movable member are integrated together. When the surface-deforming element 200 is flexed slowly, there is no movement because of a frictional force acting between the clamp legs 204 and the wall surface W. Then, when flexed reversely in a short time, a flexure force surpasses the frictional force due to an increase of acceleration force so that the actuator is moved in the acceleration direction. By the repetition of the operation, displacement takes place to enable movement within the bore.
In the meanwhile, there is a demand for the lens module for use on a cellular-phone digital camera to achieve, at low cost, such performance improvements as optical-element pixel densification, zooming and auto-focusing, and unintentional-movement prevention. However, in the background art shown in JP-A-4-69070, problems remain in size and cost reduction because of non-integral structure of the driving rod 117 and the lens barrel 101 to be displaced. Also, because the driving rod 117 is always in contact, on the same plane, with the holes 101b, 101d of the lens barrel 101 through which the driving rod 117 is passed, fixing readily occurs due to an occurrence of static electricity, etc. Moreover, because of the driving force orthogonal to fixing force, a fixing force theoretically could not be directly suppressed by a driving force, leaving a problem in respect of reliability. This is similar to JP-A-7-298654. Furthermore, the lens barrel 101 is susceptible to the effect of gravity because it hangs relative to the driving rod 117.
Still, in the art described in JP-A-8-207755, size reduction is not easy because the frictional force due to the clamp legs 204 is necessary as a holding force for the actuator. There are also problems of low displacement efficiency and low durability because the clamp legs 204 absorb the vibration of the surface-deforming element 200. Furthermore, there is a disadvantage of low displacement speed because the resonant frequency of the actuator readily lowers making it impossible to increase the driving frequency. In addition, comprising the weight 202, inertia is used to cause a movement. Thus, a discrepancy may arise between a downward movement speed and an upward movement speed, resulting in a disadvantageous variability in displacement speed.
Furthermore, each of the foregoing background arts uses, as its own holding force, the gravity acting upon the device weight or lens barrel. Accordingly, there is a dependency upon gravity during driving, and the gravity also has an influence during resting. Particularly, in the art of JP-A-8-207755, if there is a variation among the elastic forces of the clamp legs 204, a rotation may readily occur taking a direction orthogonal to the direction of displacement as an axis, making it difficult to control the position.